Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.

Patents

  1. Advanced Patent Search
Publication numberUS5268069 A
Publication typeGrant
Application numberUS 07/895,493
Publication dateDec 7, 1993
Filing dateJun 8, 1992
Priority dateOct 28, 1991
Fee statusLapsed
Publication number07895493, 895493, US 5268069 A, US 5268069A, US-A-5268069, US5268069 A, US5268069A
InventorsJonathan D. Chapple-Sokol, Richard A. Conti, David E. Kotecki, Andrew H. Simon, Manu Tejwani
Original AssigneeInternational Business Machines Corporation
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Safe method for etching silicon dioxide
US 5268069 A
Abstract
Anhydrous ammonium fluoride is used as a safe source of hydrogen fluoride for etching native or other silicon dioxide layers from silicon substrates. Heating the anhydrous ammonium fluoride above its sublimation temperature results in the generation of hydrogen fluoride gas which etches the silicon dioxide. Controlled amounts of water vapor are used during the etch reaction to ensure complete etching of the thin oxide layers down to within hundredths of a monolayer and to achieve precise etch rate control.
Images(4)
Previous page
Next page
Claims(17)
Having thus described our invention, what we claim as new and desire to secure by Letters Patent is as follows:
1. A method of etching or cleaning of silicon dioxide, comprising:
placing a silicon substrate having a silicon dioxide layer formed thereon into an etch chamber;
supplying a quantity of anhydrous ammonium fluoride in said etch chamber or in a chamber in close proximity to said etch chamber and connected therewith;
heating said anhydrous ammonium fluoride above a temperature of sublimation for said anhydrous ammonium fluoride to create a gaseous specie which is transported to and etches said silicon dioxide on said silicon substrate; and
preventing formation of an ammonium fluoride film on said silicon dioxide on said silicon substrate during said heating step.
2. A method as recited in claim 1 wherein said gaseous specie created during said heating step is hydrogen fluoride.
3. A method as recited in claim 1 wherein said heating step heats said anhydrous ammonium fluoride to 100° C. or more.
4. A method as recited in claim 1 further comprising the step of maintaining said silicon substrate at a temperature below said temperature required for sublimation of said anhydrous ammonium fluoride.
5. A method as recited in claim 1 further comprising the step of maintaining said silicon substrate at a temperature above said temperature required for sublimation of said anhydrous ammonium fluoride.
6. A method as recited in claim 1 further comprises the step of modulating the temperature of said anhydrous ammonium fluoride above and below said sublimation temperature, whereby the delivery of said gaseous specie is regulated.
7. A method as recited in claim 1 further comprising the step of depositing a layer of material on said silicon substrate immediately after said layer of silicon dioxide has been removed and before any silicon dioxide regrowth.
8. A method as recited in claim 1 further comprising the step of providing quantities of water vapor within said etch chamber.
9. A method as recited in claim 8 further comprising the step of removing quantities of water vapor from within said etch chamber.
10. A method as recited in claim 1 further comprising the step of removing quantities of water vapor from within said etch chamber.
11. A method of etching or cleaning of silicon dioxide, consisting of:
placing a silicon substrate having a silicon dioxide layer formed thereon into an etch chamber;
supplying a quantity of anhydrous ammonium fluoride in said etch chamber or in a chamber in close proximity to said etch chamber and connected therewith;
heating said anhydrous ammonium fluoride above a temperature of sublimation for said anhydrous ammonium fluoride to create a gaseous specie which is transported to and etches said silicon dioxide on said silicon substrate; and
preventing formation of an ammonium fluoride film on said silicon dioxide on said silicon substrate during said heating step.
12. A method of etching or cleaning of silicon dioxide, comprising:
placing a silicon substrate having a silicon dioxide layer formed thereon into an etch chamber;
providing quantities of water vapor within said etch chamber;
supplying a quantity of anhydrous ammonium fluoride in said etch chamber or in a chamber in close proximity to said etch chamber and connected therewith; and
heating said anhydrous ammonium fluoride above a temperature of sublimation for said anhydrous ammonium fluoride to create gaseous specie which is transported to and etches said silicon dioxide on said silicon substrate.
13. A method as recited in claim 12 wherein said step of providing quantities of water is performed prior to said step of heating said anhydrous ammonium fluoride.
14. A method as recited in claim 12 wherein said step of providing quantities of water is performed during said step of heating said anhydrous ammonium fluoride.
15. A method of etching or cleaning of silicon dioxide, comprising:
placing a silicon substrate having a silicon dioxide layer formed thereon into an etch chamber;
removing quantities of water vapor from within said etch chamber;
supplying a quantity of anhydrous ammonium fluoride in said etch chamber or in a chamber in close proximity to said etch chamber and connected therewith; and
heating said anhydrous ammonium fluoride above a temperature of sublimation for said anhydrous ammonium fluoride to create gaseous specie which is transported to and etches said silicon dioxide on said silicon substrate.
16. A method as recited in claim 15 wherein said step of removing quantities of water from within said etch chamber is repeated periodically.
17. A method of etching or cleaning of silicon dioxide, comprising:
placing a silicon substrate having a silicon dioxide layer formed thereon into an etch chamber;
providing quantities of water within said etch chamber;
supplying a quantity of anhydrous ammonium fluoride in said etch chamber or in a chamber in close proximity to said etch chamber and connected therewith;
heating said anhydrous ammonium fluoride above a temperature of sublimation for said anhydrous ammonium fluoride to create gaseous specie which is transported to and etches said silicon dioxide on said silicon substrate; and
removing quantities of water vapor from within said etch chamber.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This patent application is a continuation-in-part (CIP) patent application of the co-pending patent application having Ser. No. 07/783,857 which was filed Oct. 28, 1991, now abandoned, and that patent application is herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is generally related to a method of etching or cleaning off native or other silicon dioxide (SiO2) from the surface of a silicon (Si) substrate and, more particularly, to a safe method of etching or cleaning off SiO2 which employs anhydrous ammonium fluoride (NH4 F) as a source of hydrofluoric acid (HF) which is used for etching or cleaning off the SiO2.

2. Description of the Prior Art

If the surface of a silicon substrate is exposed to ambient air, a native SiO2 layer forms on its surface. The native SiO2 layer presents certain manufacturing difficulties since many semiconductor processes, such as low-temperature epitaxy, polysilicon deposition, and silicidation, require the silicon wafer surface to be free of all native SiO2. Over the years, many different processes for etching or cleaning off the native SiO2 from Si surfaces have been developed. One of the most commonly used techniques for etching SiO2 is to expose the substrate to HF (wet or dry). However, the use of liquid or vapor HF has major drawbacks for the semiconductor manufacturer because it is both highly toxic and highly corrosive. The high toxicity of HF requires the semiconductor manufacturer to implement safety procedures and devices which assure that personnel and the environment are not injured by the HF gas. The high corrosiveness of HF requires the semiconductor manufacturer to utilize non-corrosive storage containers and non-corrosive tubing for delivering the HF gas to a cleaning or etch chamber, and this type of equipment is generally more expensive than containers and tubing that do not have non-corrosive properties.

In U.S. Pat. No. 5,030,319 to Nishino et al. and in the article to Nishino et al., 1989 Dry Process Symposium IV-2, 90-92 (1989), a method of selectively etching native SiO2 from a silicon substrate is disclosed which employs the fluorine atoms and nitrogen hydrides produced by an NH3 and NF3 microwave discharge. In the Nishino et al. etch process, a film of (NH4)2 SiF6 is formed by condensation on the surface of the substrate by the reaction of NH4 + and F- with the polarized Si atom of the ionic SiO2 species. For film formation to occur, the substrate temperature must be maintained below 100° C., and is preferably performed at room temperature. After film formation, the substrate is heated above 100° C. and the (NH4)2 SiF6 film vaporizes to leave an oxygen free silicon surface.

The Nishino et al. etch process is not ideal because it requires the transport of corrosive and toxic gases into a reaction chamber; therefore, the cost of non-corrosive tubing and storage chambers as well as the requirement of increased safety procedures are not avoided by the Nishino et al. etch process. Moreover, the Nishino et al. process imposes timing and temperature control parameters on a semiconductor manufacturer since the wafer temperature must first be maintained below 100° C. to allow an etching film to form on the substrate surface, and subsequently, the substrate must be heated above 100° C. to remove the etch products. Nishino et al. acknowledge that if the temperature is kept above 100° C. initially, film deposition does not take place and no SiO2 etching occurs.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide a safe and non-corrosive method of removing native or other SiO2 from silicon surfaces which employs anhydrous NH4 F as a source of HF.

It is another object of this invention to provide a method of controlling the SiO2 etch rate with HF by regulating the amount of adsorbed water (H2 O) present on the SiO2.

According to the invention, anhydrous NH4 F is used as a safe source of HF to etch the native SiO2 from silicon surfaces. A supply of anhydrous NH4 F is provided either in the etching or cleaning chamber in which the silicon substrates are positioned or is provided in a chamber which is in close proximity to the etching or cleaning chamber and is connected therewith. Upon heating, anhydrous NH4 F sublimates to form HF gas and NH3 gas. The HF gas then etches off the native or other SiO2 on the surface of the silicon substrate.

Controlled amounts of water vapor are used during the etch reaction to ensure complete etching of the thin oxide layers down to within hundredths of a monolayer and to achieve precise etch rate control. Trace quantities of water aid in initiating the SiO2 etch reaction with HF and anhydrous HF vapor alone cannot be used to achieve complete etching of thin native or chemical oxides on patterned substrates where the rest of the pattern is bulk or thick oxide (see, McIntosh et al., J. of Elect. Mat., 21:57-60 (1992)). Therefore, precise quantities of water vapor are advantageously metered into the etch chamber prior to or during NH4 F sublimation for SiO2 etching. Water which is not adsorbed on the SiO2 surface is either pumped out of the etch chamber or is purged out by flowing dry inert gas over the SiO2 surface. In addition, water vapor is a by-product of the SiO2 etch reaction itself. Hence, the etch rate of subsequent oxide etches can vary from the first oxide etch if the quantity of water vapor within the etch chamber is not controlled. Therefore, periodic (e.g., after each SiO2 etch) water vapor evacuation or purging from the etch chamber assures that the etch rate remains controlled.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

Anhydrous NH4 F sublimates at temperatures above 100° C. and at pressures on the order of one to ten Torr according to the following reaction:

NH4 F.sub.(c) →HF.sub.(g) +NH3(g)

Anhydrous NH4 F is intrinsically safer than gaseous or aqueous HF because it absorbs water readily and is converted to a less reactive form, aqueous NH4 F, upon exposure to air. Aqueous NH4 F is used in making buffered HF solutions and does not form gaseous HF upon heating or evaporation. Anhydrous NH4 F is commercially available from a variety of sources including Aldrich Chemical, Sigma Chemical, and Alfa Chemical.

In the present invention, anhydrous NH4 F is provided either in the etching or cleaning chamber in which the silicon substrates having SiO2 are positioned or is provided in a chamber which is in close proximity to the etching or cleaning chamber and is connected therewith. The anhydrous NH4 F may be provided in an open or valved ampoule, container or the like. Upon heating the ampoule or container of anhydrous NH4 F above the sublimating temperature, HF gas is generated and the HF gas is used to etch the SiO2 from the surface of the silicon substrate. It is possible that the NH3 gas generated during the sublimation will also assist in the etching by acting as an electron donor in the reaction. Control of the delivery of the HF gas for etching SiO2 can be accomplished by regulating the temperature to which the ampoule or container of anhydrous NH4 F is exposed (i.e., modulating the temperature above and below sublimation temperature as HF gas is required, or similar processes). Hence, this invention avoids the problems associated with the handling and transport of HF gas by using anhydrous NH4 F as a source of HF gas in the same etch chamber as the silicon substrate or in a chamber in close proximity with and connected to the etch chamber.

In a test experiment, a silicon substrate with a thermally grown SiO2 layer was placed adjacent a container of anhydrous NH4 F. The substrate was maintained at ambient temperature, but the anhydrous NH4 F was heated to a temperature of 200° C. such that it sublimated to form HF gas and NH3 gas. The SiO2 on the substrate surface was observed to be etched at a rate of approximately 30Å/min. Similar results would be achieved when the substrate is maintained at an elevated temperature above the temperature of NH4 F sublimation.

Water vapor is advantageously added to the etch chamber to assist in the etching of the SiO2 ; however, care must be taken to prevent the anhydrous NH4 F from being converted to its aqueous form prior to generation of the HF gas.

Controlled amounts of water vapor are used during the etch reaction to ensure complete etching of the thin oxide layers down to within hundredths of a monolayer (a level suitable for epitaxy) and to achieve precise etch rate control. Trace quantities of water aid in initiating the SiO2 etch reaction with HF. Moreover, McIntosh et al., J. of Elect. Mat., 21:57-60 (1992), show that anhydrous HF vapor alone cannot be used to achieve complete etching of thin native or chemical oxides on patterned substrates where the rest of the pattern is bulk or thick oxide. Therefore, precise quantities of water vapor are advantageously metered into the etch chamber prior to or during NH4 F sublimation to HF and NH3 for SiO2 etching. Water which is not adsorbed on the SiO2 surface is either pumped out of the etch chamber or is purged out by flowing dry inert gas over the SiO2 surface.

Water vapor is a by-product of the SiO2 etch reaction itself. Hence, the etch rate of subsequent oxide etches can vary from the first oxide etch if the quantity of water vapor within the etch chamber is not controlled. Therefore, periodic (e.g., after each SiO2 etch) water vapor evacuation or purging from the etch chamber assures that the etch rate remains controlled.

For thick oxide films, a repetitive process which includes the steps of exposure to water vapor, purge or evacuation of excess water vapor, and NH4 F sublimation for HF etching of SiO2 allows for fine control over the etch rate as well as ensures complete etching down to hundredths of a monolayer levels of oxide. This degree of etching provides an adequate pre-clean for subsequent processing steps including epitaxy and polysilicon deposition. Preferably, any subsequent processing steps will be performed in the same etch chamber or another chamber vacuum connected to the etch chamber immediately after etching the SiO2 layer such that regrowth of native SiO2 is prevented.

While the invention has been described in terms of its preferred embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the appended claims.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US273588 *Oct 31, 1882Mar 6, 1883 Ernst nienstadt
US276893 *May 1, 1883 Assigeob of
US276896 *May 1, 1883 Berg-e
US382318 *May 8, 1888 Etching glass
US1470772 *Aug 21, 1922Oct 16, 1923Henry L GreenbaumPaste for etching glass
US3979241 *Mar 29, 1973Sep 7, 1976Fujitsu Ltd.Method of etching films of silicon nitride and silicon dioxide
US4459173 *Jul 22, 1983Jul 10, 1984The Dow Chemical CompanyAmmonium bifluoride
US4749440 *May 12, 1987Jun 7, 1988Fsi CorporationGaseous process and apparatus for removing films from substrates
US4761244 *Jan 27, 1987Aug 2, 1988Olin CorporationNonionic surfactants
US5030319 *Dec 27, 1989Jul 9, 1991Kabushiki Kaisha ToshibaReacting gases to produce hydrogen halide
Non-Patent Citations
Reference
1 *1989 Dry Process Symposium IV 2, Nishino et al.; 90 92; (1989).
21989 Dry Process Symposium IV-2, Nishino et al.; 90-92; (1989).
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US5766971 *Dec 13, 1996Jun 16, 1998International Business Machines CorporationForming oxide on substrate, etching to form isolation trench, filling with oxide, etching, reacting with ammonia to form nitride, etching
US5770263 *Nov 8, 1995Jun 23, 1998Micron Technology, Inc.Method for in situ removal of particulate residues resulting from hydrofluoric acid cleaning treatments
US5838055 *May 29, 1997Nov 17, 1998International Business Machines CorporationPatterned substrate for integrated circuits
US5876879 *May 29, 1997Mar 2, 1999International Business Machines CorporationDimensions in the oxide layer being etched can be specifically sized smaller than openings made in the overcoating masking material.
US5922623 *May 8, 1996Jul 13, 1999Nec CorporationEtching silicon oxide film abutting refractory metal silicide electrodes
US5972804 *Nov 3, 1997Oct 26, 1999Motorola, Inc.Process for forming a semiconductor device
US6029680 *Jun 22, 1998Feb 29, 2000Micron Technology, IncMethod for in situ removal of particulate residues resulting from cleaning treatments
US6048406 *Apr 8, 1998Apr 11, 2000Texas Instruments IncorporatedBenign method for etching silicon dioxide
US6071815 *Sep 2, 1998Jun 6, 2000International Business Machines CorporationMethod of patterning sidewalls of a trench in integrated circuit manufacturing
US6074951 *May 29, 1997Jun 13, 2000International Business Machines CorporationVapor phase etching of oxide masked by resist or masking material
US6297173Aug 26, 1999Oct 2, 2001Motorola, Inc.Process for forming a semiconductor device
US6399504 *Nov 23, 1999Jun 4, 2002Micron Technology, Inc.Cleaning semiconductor surface; using aqueous solution of ammonium fluoride, ammonium hydroxide and hydrogen fluoride mixtures
US6740247Feb 4, 2000May 25, 2004Massachusetts Institute Of TechnologyHF vapor phase wafer cleaning and oxide etching
US6838391Jul 22, 2003Jan 4, 2005Osram Opto Semiconductors Gmbh & Co. OhgMethod of semiconductor processing including fluoride
US6864112Nov 28, 2000Mar 8, 2005Osram Opto Semiconductors Gmbh & Co. OhgMethod of production of a patterned semiconductor layer
US7416989 *Jun 30, 2006Aug 26, 2008Novellus Systems, Inc.Adsorption based material removal process
US7479461 *Sep 17, 2004Jan 20, 2009Infineon Technologies AgMethod of etching silicon anisotropically
US7611995 *Apr 20, 2004Nov 3, 2009Tokyo Electron LimitedMethod for removing silicon oxide film and processing apparatus
US7977249Mar 7, 2008Jul 12, 2011Novellus Systems, Inc.Methods for removing silicon nitride and other materials during fabrication of contacts
US7981763Dec 22, 2008Jul 19, 2011Novellus Systems, Inc.Atomic layer removal for high aspect ratio gapfill
US8043972 *Jul 16, 2008Oct 25, 2011Novellus Systems, Inc.Adsorption based material removal process
US8058179Dec 23, 2008Nov 15, 2011Novellus Systems, Inc.Atomic layer removal process with higher etch amount
US8187486Dec 13, 2007May 29, 2012Novellus Systems, Inc.Modulating etch selectivity and etch rate of silicon nitride thin films
US8617348May 1, 2012Dec 31, 2013Novellus Systems, Inc.Modulating etch selectivity and etch rate of silicon nitride thin films
US20100144156 *Dec 9, 2008Jun 10, 2010Hui-Shen ShihMethod to integrate micro electro mechanical system and cmos image sensor
US20100258233 *Nov 6, 2008Oct 14, 2010Mitsubishi Materials CorporationCeramic substrate, method of manufacturing ceramic substrate, and method of manufacturing power module substrate
DE19824142A1 *May 29, 1998Dec 9, 1999Siemens AgVerfahren zum Ätzen von flourwasserstofflöslichen Schichten
WO2003098679A1 *Apr 1, 2003Nov 27, 2003IbmMethod of fabricating a bipolar transistor having a realigned emitter
Classifications
U.S. Classification216/73, 134/3, 216/79, 257/E21.226, 257/E21.252, 134/31, 257/E21.227
International ClassificationH01L21/311, H01L21/306
Cooperative ClassificationH01L21/31116, H01L21/02049, H01L21/02046
European ClassificationH01L21/311B2B, H01L21/02F2B, H01L21/02F2B2
Legal Events
DateCodeEventDescription
Jan 31, 2006FPExpired due to failure to pay maintenance fee
Effective date: 20051207
Dec 7, 2005LAPSLapse for failure to pay maintenance fees
Jun 22, 2005REMIMaintenance fee reminder mailed
Jan 8, 2001FPAYFee payment
Year of fee payment: 8
Jan 27, 1997FPAYFee payment
Year of fee payment: 4
Jun 8, 1992ASAssignment
Owner name: INTERNATIONAL BUSINESS MACHINES CORPORATION A COR
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNORS:CHAPPLE-SOKOL, JONATHAN D.;CONTI, RICHRD A.;KOTECKI, DAVID E.;AND OTHERS;REEL/FRAME:006151/0475
Effective date: 19920608